This invention relates to the epitaxial growth of crystals for the production of light emitting devices and more particularly to a process for obtaining epitaxial growth wherein a basic gallium arsenide wafer is precoated with a gallium master melt. It is then heated to effect solution of a portion of the substrate, and the entire wafer is then cooled in a manner so that it remains slightly cooler than the melt during the cooling cycle, resulting in a high quality epitaxial layer grown on the substrate.
The method first utilized in producing devices of the type concerned with in this invention is described in U.S. Pat. No. 3,158,512 wherein a flooding or dipping method is utilized for introducing an epitaxial layer on a semiconductive wafer. A method involving the liquid phase epitaxy of semiconductor material in a sandwich structure employing a temperature gradient is described in U.S. Pat. No. 3,301,716. Recently, the flooding procedure has been implemented by the procedures indicated in U.S. Pat. Nos. 3,551,219 and No. 3,560,276 wherein the surface conditions of the seed wafer are improved by use of a sliding crucible, open on both sides. The crucible is machined into a graphite block which slides over the wafer sitting in a groove of the graphite rail. These so-called conventional dipping or tipping techniques are said to be improved upon in an article entitled "The Liquid Phase Epitaxy of Aluminum Gallium Arsenide for Monolithic Planar Structures" appearing in Volume 59 No. 10 of the Proceedings of the I.E.E.E. October 1971 by Joseph M. Blum and Kwang K. Shih wherein a liquid phase epitaxial process is described for a melt containing gallium, gallium arsenide, aluminum, and a dopant which is laid above the source material inside a sliding graphite top plate.
In the previously referred to processes the surface melting conditions and temperature controls place narrow boundary limits on the success rate. In some instances, the vibration of the melt has been used to homogenize the oversaturated solution and to improve the cooling conditions. While these methods can be used for laboratory work, mass production of light emitting devices has to be based on a more reliable method of production which at the same time will have the advantage of easier handling such that less technically trained personnel can successfully achieve high quality epilayers.
It is an object of the present invention to provide a novel process for producing epitaxial depositions on a substrate in a fast and reliable manner. It is another object of this invention to provide a process for producing heteroepitaxial layers in mass production such that the substrate crystal itself serves as a saturation source. It is still another object of the present invention to provide a method for producing light emitting diodes by the epitaxial growth process wherein the epilayers are of high quality and have close tolerances yet can be performed by personnel who are not highly trained. It is yet another object of this invention to provide a unique ohmic contact which is formed during eutectic bonding of the alloy die.